Method and device for operating an internal combustion engine

ABSTRACT

The invention relates to a method for improving the thorough mixing of the exhaust gas/fuel mixture in an internal combustion engine ( 1 ), whereby the exhaust gas stream is at least temporarily impinged upon by an increased exhaust-gas mass flow when additional fuel is supplied. According to said method, during the exhaust stroke, when the exhaust valve ( 8 ) or exhaust valves are open, the additional fuel is fed directly into the combustion chamber of the internal combustion engine ( 1 ). The invention also provides for a device to carry out said method, according to which the additional fuel is injected during the exhaust stroke when the exhaust valve ( 8 ) or exhaust valves ( 8 ) are open by means of at least one injection nozzle ( 10 ) positioned in the combustion chamber. Both the method and the device are especially simple and cost-efficient.

This invention relates to a process and a device for operation of aninternal combustion engine in which an increased exhaust gas mass flowacts at least temporarily on the exhaust gas stream.

A process such as this and a device for application of the process aredisclosed in German publication DE 41 39 291 A1, for example. In thisprocess, in order to achieve improved exhaust gas decontamination andfaster acceleration of the exhaust gas turbine in the area of theexhaust gas manifold, an increased amount of fuel is delivered which isspark ignited a short distance upstream from the gas turbine. Thisprocess and the device applying it do, however, present the disadvantagethat the additional fuel cannot be distributed in the exhaust gas withadequate efficiency and that costly mechanisms for delivery and ignitionof the additional fuel must be provided in the exhaust gas stream.

In addition, publications WO 96/03572 and DE 196 22 832 A1 describe aprocess and a device for increasing the efficiency of a catalyticconverter in a diesel engine in which secondary injection must becarried out in addition to the primary injection during the exhauststroke of the engine. The additional fuel is introduced in this case bythe engine fuel injection device into the cylinders and ignitesspontaneously in the latter.

It is the object of this invention to develop the state-of-the-artprocesses so as to permit improved intermixture and simplified ignitionof the fuel-exhaust gas mixture. An additional object is provision of adevice for application of the process developed.

The object claimed for the process is attained by means of the featuresdescribed in claim 1. Better intermixture of additional fuel withresidual gas is accomplished by supply of additional fuel during theexhaust cycle with the exhaust valve or valves open, directly into thecombustion chamber of the internal combustion engine filled withresidual gas, since the optimized geometries present in the combustionchamber may be used for this purpose. As a result of the improvedintermixture, the pressure and the temperature of the exhaust gas of theadditional fuel and the residual gas are improved in such a way that theresponse characteristic of an exhaust gas turbine is distinctlyimproved. In addition, a catalytic converter optionally provided in theexhaust gas stream can, as a result of increase in pressure andtemperature of the exhaust gas, reach its operating temperature morequickly and retain this temperature even under unfavorable conditions.Such unfavorable conditions exist in particular during overrunningoperation of the internal combustion engine, since normal fuel deliveryis then discontinued, as a result of which there is a risk both of dropin the speed of the exhaust gas turbine and of lowering of thetemperature of the catalytic converter. And, because the additional fuelis spark ignited, afterburning of the additional fuel is ensured in anyevent.

By preference delivery of additional fuel takes place before the pistonof the internal combustion engine reaches the gas exchange upper deadcenter (OT=oberer Totpunkt). As a result, sufficient time still remainsfor intermixture of the additional fuel with the residual gas and forthe mixture to leave the combustion chamber through the opened dischargevalve. If, on the other hand, the additional fuel has already burnedbefore the piston reaches the gas exchange OT, this even causes a slightdelay of the piston stroke. In theory delivery of additional fuel in acrankshaft angle range of approximately 120 to 380 degrees beyond theignition OT is conceivable.

Additional fuel should be delivered with intake valves closed. In thisway the mixture of additional fuel and residual gas cannot reach theintake stream of the internal combustion engine, as a result of whichthe efficiency of the internal combustion engine would be impaired. Inaddition, the time of opening of the intake valves of the internalcombustion engine may be displaced in the direction of “retarded” atleast temporarily, that is, during delivery of additional fuel. Thereason is that this has the effect of lengthening the interval betweenopening of the discharge valve and opening of the intake valve, so thatmore time is accordingly available for delivery of the additional fueland intermixture of the additional fuel with the residual gas.

The additional fuel is injected in a suitable manner during the coldoperation stages, the acceleration stages, and/or with the internalcombustion engine under low load, that is, in overrunning operation aswell. Improvement in the response characteristic of the exhaust gasturbine, as well as faster heating or constant heating of the exhaustgas catalytic converter, are, after all, desirable especially underthese operating conditions.

The residual gas in the combustion chamber of the internal combustionengine should have excess air immediately before delivery of theadditional fuel, so that additional fresh air need not be delivered byanother route for afterburning of the mixture of additional fuel andresidual gas. For example, the throttle valve, open during overrunning,could be closed on the basis of the speed of the internal combustionengine in order to obtain residual gas with sufficient excess air.

Additional fresh air could, of course, also be delivered by anotherroute for the afterburning. For example, fresh air from the intakestream could be diverted and introduced into the exhaust gas stream asclose as possible to the combustion chamber upstream from the closedthrottle valve during overrunning operation. Delivery of additionalfresh air could in the process be controlled on the basis of the intakepressure of the exhaust gas turbine, the speed of the internalcombustion engine, and/or the time derivative of engine speed(acceleration or retardation).

The amount of additional fuel is determined in the process claimed forthe invention on the basis of the excess air in the amount of residualgas and/or the amount of additional fuel delivered.

The object claimed for the device is attained by the features describedin claim 9. Through injection of the additional fuel by means of atleast one injection nozzle mounted in the combustion chamber, thedirect-injection nozzles by definition present in the combustion chamberof Otto internal combustion engines may be used, so that no additionalmechanisms are required for delivery of the additional fuel. Inaddition, the electronic drive unit already present may be used for theinjection nozzles.

Preferably at least one injection valve is mounted on the cylinder headside in the internal combustion engine for injection of additional fuel.Consequently, additional fuel may be delivered by an especiallyadvantageous method also a short time before the piston of the internalcombustion engine reaches the gas exchange OT.

It is claimed for the device that residual gas with a great amount ofexcess air can be provided and/or fresh air can be diverted from theintake upstream of a throttle valve and injected into the exhaust gasstream as close as possible to the combustion chamber so that reliableafterburning is ensured.

In an advantageous embodiment of this invention, external ignition ofthe mixture of additional fuel, residual gas, and/or additional freshair is effected by means of at least one ignition plug mounted in thecombustion chamber of the internal combustion engine. Consequently, atleast the ignition plug by definition present in Otto internalcombustion engines may be used, so that no other mechanisms are requiredfor ignition of the additional fuel. In this instance as well theelectronic triggering unit for the ignition plugs already present may beused.

It is especially preferable to have at least the single ignition plugmounted in the combustion chamber for external ignition of the mixtureof additional fuel, residual gas, and additional fresh air on thecylinder head side.

This invention is described in detail with reference to the followingdrawing.

The FIGURE of the drawing shows a diagrammatic representation of afour-cylinder reciprocating internal combustion engine 1 with aturbocharger 2 and catalytic converter 3.

The four cylinders 4 of the internal combustion engine 1 are adjacent onthe intake side to an intake distributor 5 and on the discharge side toan exhaust gas manifold 6.

Two intake valves 7 and two discharge valves 8 are assigned to eachcylinder 4 for charge changing. These valves 7, 8 are mounted in thecylinder head 9 of the internal combustion engine 1. Also mounted in thecylinder head 9 of the internal combustion engine 1 are, for example,two injection nozzles 10 and one spark plug 11 per cylinder 4. Theseinjection nozzles 10 are mounted symmetrically on both sides of thespark plugs 11, in the center of the cylinders 4, between the intakevalves 7 and the discharge valves 8.

The internal combustion engine 1 operated by the four-cycle process innormal operation uses the two injection nozzles 10 present for directinjection of Otto fuel and the spark plug 11 for ignition of the mixtureof fuel and fresh gas formed in the combustion chamber of the internalcombustion engine 1.

The discharge cycle begins after ignition and burning of the fuel andfresh gas mixture, the two intake valves 7 being closed and the twodischarge valves 8 being open. During the discharge cycle, shortlybefore the piston, not shown, of the internal combustion engine 1reaches its upper dead center (OT), one or both of the injection nozzles10 inject(s) a small amount of additional fuel into the combustionchamber in the cylinder 4, which fuel spontaneously ignites because ofthe excess air in the hot residual gas or is simply spark ignited by anadditional spark of the spark plug 11.

The afterburning mixture of additional fuel and residual gas is thendisplaced past the open discharge valves 8 into the exhaust manifold 6,such displacement being supported by the further movement of the pistontoward the upper dead center (OT).

To prevent the mixture of additional fuel and residual gas from alsomoving past the intake valves 7 to reach the intake distributor 5, theactuating times are set so that the opening periods of the intake valves7 and the discharge valves 8 do not overlap during injection of theadditional fuel and residual gas. The opening times of the intake valves7 are for this purpose displaced slightly toward “retarded.”

As a result of injection of the additional fuel, the mixture reachingthe exhaust manifold 6 possesses increased exhaust energy, it beingmanifested in particular in rise in pressure and temperature. Thisincreased exhaust gas energy results in a better response characteristicin the lower engine speed range for the exhaust gas turbocharger 2adjacent to the exhaust manifold 6. The increased exhaust gas energyalso makes it possible for the catalytic converter 3 shown in the FIGUREadjacent to the exhaust gas turbocharger 2 to be heated more rapidly toits operating temperature and for the catalytic converter 3 to retainthis temperature more efficiently. In this way sulfur contaminationoccurring in catalytic converters for lean-mix engines can beneutralized.

The arrows in the FIGURE indicate the direction of flow of fresh airdrawn in and, accordingly, the direction of the exhaust gases expelled.

What is claimed is:
 1. A process for operating an internal combustionengine, comprising of: delivering an additional amount of fuel with anincreased exhaust gas mass flow acting temporarily on an exhaust gasstream, wherein the additional amount of fuel is delivered directly to acombustion chamber of the internal combustion engine during a dischargecycle with discharge valve and a plurality of valves open and theadditional fuel is spark ignited.
 2. The process as claimed in claim 1,wherein delivery of the additional amount of fuel takes place before apiston of the internal combustion engine reaches an upper dead center.3. A process as claimed in claim 1, wherein the delivery of theadditional amount of fuel takes place with one of an intake valve and aplurality of intake valves closed.
 4. The process as claimed in claim 3,wherein an opening time for one of the intake valve and the plurality ofintake valves of the internal combustion engine is displaced toward aretarded direction during the delivery of the additional amount of fuel.5. The process as claimed in claim 1, wherein the additional fuel beingdelivered to the internal combustion engine during one of cold runningstages, acceleration stages and a warmed-up stage under low load.
 6. Theprocess as claimed in claim 1, wherein residual gas in the combustionchamber of the internal combustion engine has one of an excess of airand additional fresh air is delivered to the exhaust gas streamimmediately before delivery of the additional amount of fuel.
 7. Theprocess as claimed in claim 6, wherein an amount of additional fuel isdetermined based on one of an amount of residual gas, an amount ofexcess air in a plurality of cylinders of the internal combustion engineand an amount of additional fresh air delivered.
 8. The process asclaimed in claim 1, wherein ignition of a mixture of one of theadditional amount of fuel, an amount of residual gas, and an additionalamount of fresh air takes place inside the combustion chamber of theinternal combustion engine.
 9. A device for applying the processdescribed in claim 1, wherein the additional amount of fuel is deliveredby at least one injection nozzle mounted in the combustion chamber. 10.The device as claimed in claim 9, wherein at least one injection nozzlefor injecting the additional amount of fuel is mounted on acylinder-head side in the combustion chamber.
 11. The device as claimedin claim 10, wherein the mixture of one of the additional amount offuel, the amount of residual gas, and the additional amount of fresh airis spark-ignited by at least one spark plug mounted in the combustionchamber of the internal combustion engine.
 12. The device as describedin claim 11, wherein at least the one spark plug for external ignitionof the mixture of one of the additional fuel, the amount of residualgas, and the additional amount of fresh air is mounted on the cylinderhead-side in the combustion chamber.